A large number of roof support systems exist for use in underground mines (coal and metalliferous) and slope stabilisation.
The principal means of operation of these existing systems involves the development of a hole into the material being supported and the later introduction of a dowel or bolt. This bolt is fixed into the ground (incl. rock) using a range of systems. The fixing system is normally indicated in the name of the bolt system, for example:
(a) Chemical Anchor Bolt--where the solid bolt is fixed in place using a two part resin. PA1 (b) Split Set Bolt--where an oversized tubular bolt, with a slit in the wall (along its length) is forced into the hole, and remains in place due to the friction of the bolt with the sides of the hole. PA1 (c) Cement Grouted Bolt--this is a bolt which is inserted into a hole that is subsequently filled or had been filled with inorganic cement grout. The bolt is fixed in place when the grout sets. PA1 (d) Swellex Bolt--where an undersized capped tube is inserted in to the hole and high pressure water is used to inflate the bolt to a size which holds it firmly in place in the hole. PA1 (e) Split Wedge Bolt--point anchored mechanical bolt, which is held in place through the action of a wedge driven in to the end of the bolt at the end of the hole. PA1 (f) Expansion Shell Bolt--point anchored mechanical bolt which is held in place through the action of an internally threaded conical nut forcing serated wedges into contact with the sides of the hole. PA1 (a) Set up of drilling machines. PA1 (b) Drill hole to required depth (maximum depth=height of tunnel). PA1 (c) Remove drill steel. PA1 (d) Insert chemical or other grouting/securing medium. PA1 (e) Insert bolt. PA1 (f) Mix grout with bolt--or fix mechanical anchor. PA1 (g) Wait for grout to set. PA1 (h) Tighten bolt. PA1 (i) Pack away drilling machines. PA1 (a) drilling said bolt into said earth, rock or the like material; PA1 (b) urging of a liquid cement through the center of the bolt from the rear end of the bolt through to and beyond the leading end of the bolt such that said liquid cement reaches at or near the outer surface of said bolt. PA1 (a) drilling said bolt into said earth, rock or the like material, and a lubricating fluid being supplied to a cutting tip of said bolt during drilling through the center of the hollow bolt; PA1 (b) urging of a liquid cement through the center of the hollow bolt from the rear end of the bolt through to and beyond the cutting tip of the bolt such that said liquid cement reaches at or near the outer surface of said bolt; and PA1 (c) tensioning of said bolt.
Some of the existing systems, particularly those used in the coal mines, have the ability to be tensioned during or at the completion of fixing. This is achieved by threading the end of the bolt, and tightening a nut against a plate to apply a compressive load to the roof rock, at the same time, tensioning the bolt.
Most of the bolts in current use have some pattern or shape that increases their adhesion to the sides of the hole. The patterns are either knurling (similar to that used for reinforcing bar), "V" threading or distortion of the final shape (wiggle tail bolts etc.).
The technique of installation of the existing bolts is described in point form as:
This cycle is repeated every 0.5 to 1.5 meters of tunnel advance in coal mines, and every 3 to 200.0 meters of tunnel advance in metalliferous mines.
The main drawback of the existing systems is the number of steps involved and the time taken to install the bolt.